Much of refinery processing involves reaction of refinery streams in a hydrogen atmosphere. In order to maximize conversion efficiencies and to maintain catalyst life, excess hydrogen is generally used in the catalytic conversion processes, with the unreacted hydrogen being recovered, purified and repressurized for use as a recycle stream. Such recycle processes are costly, both in energy and in equipment. Some progress has been made in developing methods for using a single hydrogen loop in a two-stage reaction process.
U.S. Pat. No. 5,114,562 teaches a multi-reactor zone process for the production of low aromatics, low sulfur jet fuel or diesel fuel. The two reaction zones, one for desulfurization and one for hydrogenation, operate in a series flow arrangement with a common hydrogen supply system. This process uses strippers to remove H.sub.2 S from cooled hydrogen rich gases recovered from effluent streams, to permit use of the stripped hydrogen stream in both the desulfurization reaction zone and the hydrogenation reaction zone.
U.S. Pat. No. 5,403,469 teaches a parallel hydrotreating and hydrocracking process. Effluent from the two processes are combined in the same separation vessel and separated into a vapor comprising hydrogen and a hydrocarbon-containing liquid. The hydrogen is shown to be supplied as part of the feedstreams to both the hydrocracker and the hydrotreater.
U.S. Pat. No. 3,172,836 teaches a general process for processing a hydrocarbon feed in a catalyst bed, passing a liquid fraction from a first catalyst bed, together with hydrogen, through a second catalyst bed, separating the effluent from the second catalyst bed into a liquid portion and a vapor portion. The vapor portion is combined with the hydrocarbon feed in the first catalyst bed.
U.S. Pat. No. 4,197,184 discloses a conventional multiple-stage process for hydrorefining and hydrocracking a heavy hydrocarbonaceous charge stock. In the process, hydrocracked effluent is admixed with hydrorefined effluent and the combination separated into a hydrogen rich vaporous stream and normally liquid material. The cooled vapor stream is then used as a source of hydrogen and as a quench fluid for both the hydrorefining reaction zone and the hydrocracking reaction zone.
EP 787,787 discloses a hydroprocess in parallel reactors, with hydrogen flowing in series between the reactors. Effluent from a first reaction zone is separated into a first hydrogen rich gaseous stream and a first hydroprocessed product stream. The first hydrogen rich gaseous stream is shown as being used as quench for a second reaction zone. The first hydrogen rich gaseous stream is also combined with a second hydrocarbon feedstock and fed to the second reaction zone, at a lower hydrogen partial pressure than is the first reaction zone. Effluent from the second reaction zone is separated, the second hydrogen rich gaseous stream being recycled to the first reaction zone, both as a quench stream and as a reactant in combination with a first hydrocarbon feedstock.